klk720 - department of electrical & computer engineering
TRANSCRIPT
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IMPROVING PEDESTRIAN SAFETY AT SIGNALIZED INTERSECTIONS
Final Report
KLK720
N12-04
National Institute for Advanced Transportation Technology
University of Idaho
Richard W. Wall, Denise H. Bauer
June 2012
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DISCLAIMER
The contents of this report reflect the views of the authors,
who are responsible for the facts and the accuracy of the
information presented herein. This document is disseminated
under the sponsorship of the Department of Transportation,
University Transportation Centers Program, in the interest of
information exchange. The U.S. Government assumes no
liability for the contents or use thereof.
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1. Report No. 2. Government Accession
No.
3. Recipient’s Catalog No.
Title and Subtitle
Improving Pedestrian Safety at Signalized Intersections
4. Report Date
June 2012
5. Performing Organization
Code
KLK720
6. Author(s)
Dr. Wall, Richard and Dr. Bauer, Denise
7. Performing Organization
Report No.
N12-04
8. Performing Organization Name and Address 9. Work Unit No. (TRAIS)
National Institute for Advanced Transportation Technology
University of Idaho
PO Box 440901; 115 Engineering Physics Building
Moscow, ID 83844-0901
10. Contract or Grant No.
DTRT07-G-0056
11. Sponsoring Agency Name and Address
US Department of Transportation
Research and Special Programs Administration
400 7th Street SW
Washington, DC 20509-0001
12. Type of Report and Period
Covered
Final Report: August 2010
– June 2012
13. Sponsoring Agency Code
USDOT/RSPA/DIR-1
14. Supplementary Notes:
15. Abstract:
Our research investigated methods and technologies to make signalized intersections safer for pedestrians using the capabilities
of accessible pedestrian systems. Our research focused on three technologies: acoustic beaconing, passive pedestrian detection,
and pedestrian preemption. The effectiveness of proposed enhancements was measured by engineering performance analysis,
pedestrian and traffic agency feedback, and an open forum one-day workshop involving constituents of pedestrian advocacy
groups. The engineering performance analysis studied both the equipment and user interface from a human factors perspective.
The experiments were completed using existing Advanced Accessible Pedestrian Signals (AAPS) hardware. Human factors
studies were completed to determine the human response to information presented in both audible and visual format.
The changes for improved safety listed below are subject to the consideration of numerous factors before an intersection is
equipped with the capability or technology.
1. Audio beaconing is a low cost but highly effective method to direct pedestrians to the destination curb. AAPS
hardware modifications are needed to be most effective.
2. Passive pedestrian detection is simple to interface to the existing AAPS equipment but equipment costs are high
relative to the AAPS equipment.
3. Information conveyed during preemption must have a low cognitive load and unambiguous interpretation.
16. Key Words:
Pedestrian; accessible; APS; low
visions; detection;audible; human
factors
17. Distribution Statement
Unrestricted; Document is available to the public through the
National Technical Information Service; Springfield, VT.
18. Security Classif. (of
this report)
Unclassified
19. Security Classif. (of
this page)
Unclassified
20. No. of
Pages
21
21. Price
…
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
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Improving Pedestrian Safety at Signalized Intersections i
TABLE OF CONTENTS
EXECUTIVE SUMMARY ...................................................................................................... 1
DESCRIPTION OF PROBLEM............................................................................................... 3
Audio Beaconing .............................................................................................................. 4
Passive Pedestrian Detection ............................................................................................ 5
Preemption and Pedestrian Signals ................................................................................... 6
Audio Beaconing ............................................................................................................ 11
Passive Pedestrian Detection .......................................................................................... 13
Audio Beaconing ............................................................................................................ 16
Passive Pedestrian Detection .......................................................................................... 17
Preemption and Pedestrian Signals ................................................................................. 18
Appendix ................................................................................................................................. 22
PED ACCESS WORKSHOP AGENDA............................................................................ 22
References ............................................................................................................................... 23
FIGURES
Figure 1. Optimal placement of APS pushbuttons [11] ............................................................ 4
Figure 2. Advanced Pedestrian Controller block diagram ........................................................ 7
Figure 3. APC unit .................................................................................................................... 8
Figure 4. University of Idaho laboratory equipment used for pedestrian control research .... 10
Figure 5. Typical APS pedestrian station (courtesy of Campbell Company, Boise, ID) ....... 11
Figure 6. Block diagram of Advanced Pedestrian Button with added capability for second
speaker .................................................................................................................................... 12
Figure 7. Passive detection interface circuit ........................................................................... 13
Figure 8. Preemption test circuit and APC AC sense circuit .................................................. 14
Figure 9. Results for the fire engine preemption symbol........................................................ 19
Figure 10. Results for the ambulance preemption symbol ................................................. 1919
Figure 11. Results for the police car preemption symbol ....................................................... 20
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Improving Pedestrian Safety at Signalized Intersections ii
TABLES
Table 1. Results from the preemption audible message survey .............................................. 20
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Improving Pedestrian Safety at Signalized Intersections 1
EXECUTIVE SUMMARY
We have investigated technologies that are intended to reduce personal risk for pedestrians at
signalized intersections. Our research assumes that improving safety for one class of
pedestrians will result in improved safety for all pedestrians. However, we realize there are
inherent risks associated with allowing technology to remove the need for personal
responsibility to determine risk. The 2001 report “Embedded, Everywhere” recognizes the
risk of indiscriminate application of technology in the statement “There are few, if any,
ethically neutral technologies.”[1] Therefore, the questions we centered our research around
are what to do and how to do it.
We investigated three concerns of traffic agencies who are currently using or who are
considering using Accessible Pedestrian Systems (APS). All testing was conducted using the
AAPS developed at the University of Idaho and manufactured by Campbell Company. The
three major concerns of these agencies are acoustic beaconing, passive detection, and
pedestrian signal operations in the event of intersection preemption.
Acoustic beacons are audible tones that are generated at the destination curb. The target
beaconing method offers good orientation assistance and less audible distraction for low
vision pedestrians who are attempting to focus on other audible cues. Multiple speakers are
required to direct the audible message or tones. There is ongoing research to determine the
best positioning of the beacon speaker, the timing of the message or signal tones, and the
content of the message or tone frequency. Audible countdowns during the pedestrian
transition interval have been proposed. Integrating the second speaker into the AAPS will
require both hardware and software changes.
Passive pedestrian detection has advantages for physically impaired and low vision
pedestrians in that they are not required to make physical contact with the pedestrian button.
We successfully integrated the Traficon Safewalk [2] system to detect the presence of
pedestrians at the curbside. We also integrated the Traficon TraffiCam [3] system to monitor
the presence of a pedestrian in the crosswalk. There is a risk that common use of passive
video detection can lull pedestrians into unsafe behavior from lack of proper attentiveness.
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Improving Pedestrian Safety at Signalized Intersections 2
Our research concluded that the benefit comes at a high cost for the detection equipment. We
are investigating other solutions that provide non-contact activation at a much lower cost.
Preemption is an event that disrupts the normal traffic signal timing. The two most common
types of preemption are railroad and emergency vehicle. The MUTCD states that the
pedestrian clearance (pedestrian change interval) interval may be “abbreviated.” This has a
negative safety effect on disabled and low vision pedestrians. The Advance Pedestrian
Controller (APC) unit in the AAPS systems has two inputs designated to function as
preemption inputs. The two major concerns are what the pedestrian button audible message
should be during the preemption interval and the timing of those messages.
Currently, the common display during preemption follows MUTCD Section 4E.07 Paragraph
10:
“If the pedestrian change interval is interrupted or shortened as a part of a transition
into a preemption sequence (see Section 4E.06), the countdown pedestrian signal
display should be discontinued and go dark immediately upon activation of the
preemption transition.”
There is no mention of what preemption audible message should be heard in the MUTCD.
Therefore, we are investigating possible audible as well as visual messages that will inform
pedestrians of a possible dangerous situation if they are to remain in or enter the intersection.
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Improving Pedestrian Safety at Signalized Intersections 3
DESCRIPTION OF PROBLEM
The definition of pedestrian must be expanded from the classical meaning to address the
population who are served by the pedestrian controls at signalized intersections. Common
traffic signals combine vehicle movements with pedestrian movements. Right and left
turning vehicles will frequently conflict with a permitted pedestrian movement. For this
instance, the vehicle is legally obligated to yield to the pedestrian since he or she is the most
vulnerable party. If the law can make us safe, why were there 47,700 pedestrians killed
between 2000 and 2009? [4] North Carolina reports that approximately 2,500 car accidents
involving pedestrians happen every year. On average, more than 400 pedestrians are either
killed or injured severely in North Carolina pedestrian accidents annually. The internet is
replete with anecdotal accounts describing the use of personal electronic devices contributing
to pedestrian injuries [4]. The basic question becomes, “How can technology improve
pedestrian safety with minimal adverse affects?”
Blindness of varying degrees affects more than three million Americans over 40 and that
number will double by 2030 [5]. Accessible pedestrian signals (APS) are intended to provide
information concerning traffic conditions and intersection operations using three sensory
modes: auditory, tactile, and visual. Vision impaired pedestrians desire the information to be
succinct and unambiguous so that they can focus their attention on sensing what is happening
in their environment using other auditory and tactile cues.
When dealing with pedestrians, we also cannot always assume that people who have normal
visual acuity will see the dangers in crossing at intersections. Although alcohol seems to be a
cause in 12 percent of pedestrian-involved accidents, distraction is likely another leading
cause of walkers being struck by a vehicle [6]. More recently, researchers now refer to
“inattention” as “selective attention” and declare that the ability for humans to “multi-task” is
a myth and to attempt to do so in critical situations is dangerous [7]. The study of the
psychology of inattentional blindness has shown it is responsible for many errors with
serious consequences [8].
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Improving Pedestrian Safety at Signalized Intersections 4
Hence, a distraction that causes attention to be diverted can either have a positive or negative
impact on safety. Our research attempts to evaluate three specific technologies applied to
pedestrian control systems and identify both positive and negative attributes associated with
using them: audio beaconing, passive pedestrian detection, and preemption warnings.
Audio Beaconing
Audio beaconing refers to the use of an audible tone generated at the destination curb or
sidewalk to help guide the pedestrian in a straight line from his present position [9]. This has
nothing to do with beacons as discussed in the Section 4F.01 of the MUTCD or Rectangular
Rapid Flashing Beacons (RRFB) [10]. Figure 1 illustrates the recommended placement of
APS pushbuttons. It is obvious from Figure 1 that the direction of the speaker used for the
locator tone is orthogonal to the intended crosswalk. The purpose of the speaker is to help
pedestrians locate the pushbutton, and the best practices guide suggests that the audible range
be in order of 10 feet. Clearly, the placement and the volume settings suggest that using this
speaker is not suitable for beaconing that provides orientation help for pedestrians.
Figure 1. Optimal placement of APS pushbuttons [11]
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Improving Pedestrian Safety at Signalized Intersections 5
The MUTCD does not address this feature for APS systems and there is little guidance
available as to what audible message or tones should be played to provide this service. As
previously discussed, an audible signal must be a useful distraction and limited in duration to
allow the listener to return to focusing on conventional audible navigational cues. Clearly
text based messages require higher cognitive loading to mentally process the message.
Another factor that must be considered is the effect by and on the environment. If a broad
beamed audio signal is emitted, then one must consider the effects of echoes off buildings
and vehicles at the intersection. An audible signal at a low volume level may not be
detectable across the intersection in the presence of high ambient noise. An audible signal at
a high volume level intensifies the acoustic reflection problem as well as raises the potential
for objection by homeowners and business operators in the proximity of the crosswalk.
Passive Pedestrian Detection
While the transition interval is timed based upon an assumed walking speed and the length of
the crosswalk, typically, the walk interval is limited to five to seven seconds regardless of the
time allotted to the green time for the parallel traffic. This practice may be used to platoon
pedestrian traffic such that all of the pedestrian crosswalk occupancy is limited to a portion
of the total green time. The remaining green time can be used for right turn on red vehicle
movements that would not be in conflict with pedestrian movements. The second reason is
that the total green time may not be known at the end of the walk interval because green time
extensions are based upon the current traffic conditions.
The challenge for blind or mobility-impaired persons is to move from the button location to
the curb where they are to initiate their crossing [12]. It is quite common for the traffic
controller to begin the walk interval immediately after the button is pressed. Hence, part of
the walk interval is consumed by the pedestrian just getting to the crosswalk. The
construction of the intersection can be such that a blind or mobility impaired pedestrian
cannot reach the crosswalk in the allotted walk interval.
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Improving Pedestrian Safety at Signalized Intersections 6
Passive pedestrian detection has advantages for physically impaired and low vision
pedestrians in that they are not required to make physical contact with the pedestrian button
[13]. A report in 2005 indicated that false detection was a serious concern in the broad
deployment of passive detections systems [14]. Our research focused on the interface of the
Traficon Safewalk and Traficam systems [3,4] with APB devices to determine the detection
capability, effectiveness, and what information is available from an existing commercialized
passive pedestrian detection system.
Preemption and Pedestrian Signals
Preemption is the disruption of normal traffic control timing plans and is usually initiated for
approaching emergency vehicles and railroad trains. The MUTCD is very clear and concise
on the transition from normal traffic control operations and operations that serve preemptive
operations. Intersection operation during preemption events is generally part of the traffic
controller programming. Although feedback from Campbell Company suggests some traffic
agencies are requesting an input to the APC that can be used to monitor preemption type
events, there has been no clear direction from these agencies as to what to do for these
events.
When considering the response of visual and audible pedestrian signals, it is good to consider
what information is available for use. Figure 2 shows the block diagram of the APC unit
shown in Figure 3. Visual pedestrian signals are driven from load switches that transform
low voltage binary signals to switching 120 VAC outputs on and off. The load switches are
also used to control the on-off condition of the green, amber, and red traffic lights as well. In
TS2 traffic controller cabinets, the load switches can be set to switch on the 120 VAC output
during either the positive half, negative half, or both halves of the voltage waveform to
control the signal power consumption and/or luminescence. The traffic controller is
programmed to use selected load switches for the WALK and DON’T WALK signals. The
load switch alternates between the on and off condition at approximately a one hertz rate
during flash conditions. The only information that the APC has access to is the voltages that
are applied to the WALK and DON’T WALK signals.
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Improving Pedestrian Safety at Signalized Intersections 7
TS7370
Single
Board
Computer
with Linux
Operating
Systems
Interface Board
Ethernet
over Power
Line (EoP)
Modem
APC
Power
Converter
120/18 VAC
Transformer
120 VAC
Power
I2C
CO
MM
Eth
ern
et
#2 Ethernet
#1
Electronic
Relays
AC
Voltage
Sensors
Advanced Pedestrian Controller
LED
Control
5V
DC
18VAC to
APBs
Load
Switch
Outputs
Pedestrian
Detector
Inputs
Figure 2. Advanced Pedestrian Controller block diagram
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Improving Pedestrian Safety at Signalized Intersections 8
Figure 3. APC unit
The MUTCD specifies the pedestrian signal timing for transitioning into, during, and out of
preemption operations.1 The effects of these operations are only observable at the load switch
outputs; there is no useful audio information available for a blind pedestrian who is unable to
comprehend visually the reason for the change in operations. In addition, the MUTCD does
not specifically address a preemption audible message. The lowest risk pedestrian operation
is to indicate audibly the status of the pedestrian signal. Hence, the audible response to a
1 MUTCD Section 4D.27, Paragraph 08, Standard: B. “The shortening or omission of any pedestrian walk interval and/or
pedestrian change interval shall be permitted.” This statement appears to be in conflict with Paragraph 10, “During priority
control and during the transition into or out of priority control: B. The shortening of any pedestrian walk interval below that
time described in Section 4E.06 shall not be permitted. C. The omission of a pedestrian walk interval and its associated
change interval shall not be permitted unless the associated vehicular phase is also omitted or the pedestrian phase is
exclusive. D. The shortening or omission of any pedestrian change interval shall not be permitted. Section 4E:06 Paragraph
7: “Except as provided in Paragraph 08, the pedestrian clearance times should be sufficient to allow a pedestrian crossing in
the sidewalk who left the curb or shoulder at the end of the WALKING PERSON … signal condition to travel at a walking
speed of 3.5 feet per second to at least the far side of the traveled way….” Section 4E.06, Paragraph 08: “A walking speed
of up to 4 feet per second may be used to evaluate the sufficiency of the pedestrian clearance time at locations where an
extended pushbutton press has been installed ….”
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Improving Pedestrian Safety at Signalized Intersections 9
pedestrian button pressed when the walk signal is not on is the message “WAIT” or the
extended APS wait message that includes additional location information.
It is helpful to consider the pedestrian signal operations from a blind or low vision person’s
perspective. In some localities, emergency vehicles do not operate their sirens unless they are
in the immediate vicinity of an intersection or otherwise impeded. The emergency vehicles
will activate the preempted signal operations several hundred yards from the intersection.
Consequently, the emergency vehicles are operating in a stealth mode for the visually
impaired pedestrian. This can lead to a dangerous situation where a visually impaired
pedestrian may step off the curb into the oncoming emergency vehicle’s path. This appears to
have a higher probability of occurrence than with a pedestrian with normal acuity. Another
possible dangerous situation occurs even when the emergency vehicle sounds its siren and a
deaf pedestrian may have his or her vision blocked from seeing the approaching emergency
vehicle. Therefore, the question is how to deal with these potential dangerous and deadly
situations.
The MUTCD reference cited in the footnote does offer some confusion as to whether the
pedestrian change interval can or cannot be altered for preemption. The pedestrian signals are
under the control of the traffic controller and not AAPS. However, we asked ourselves, “If
we could display something to the pedestrian on the walk signal or provide an audible
message using the beaconing speaker, what would be the most helpful information to
provide?”
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Improving Pedestrian Safety at Signalized Intersections 10
APPROACH AND METHODOLOGY
All hardware and software experiments were performed in the University of Idaho Digital
Research Laboratory. The traffic control equipment shown in Figure 4 consisted of a TS2
Type I controller cabinet, an In ASC TS2 traffic controller (Econolite Controls Inc.,
Anaheim, CA), a MMU-16LEIp malfunction management unit, (Eberle Design Inc.,
Phoenix, AZ), and Model 262 loop detector (Diablo Controls, Inc., Crystal Lake, IL). The
pedestrian controls also shown in Figure 4 are the Advanced Accessible Pedestrian Systems
designed at the University of Ida ho [15] and are being produced and distributed by
Campbell Company, Boise ID.
Figure 4. University of Idaho laboratory equipment used for pedestrian control research
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Improving Pedestrian Safety at Signalized Intersections 11
Audio Beaconing
The Campbell Company pushbutton shown in Figure 5 of the appendix was used for our
research and is typical of APS pedestrian stations. It consists of a pressure activated
mechanical or piezo-electric button that is designed to have a raised arrow that indicates the
direction to the crosswalk for the intended crossing. The button is constructed on a surface
that vibrates when the walk signal is active. The light emitting diode (LED) immediately
above the button provides visual feedback to the pedestrian that a signal has been sent to the
traffic controller indicating that a pedestrian requested a walk signal.
Figure 5. Typical APS pedestrian station (courtesy of Campbell Company, Boise, ID)
To add a second speaker, the electronics required modification as illustrated by the shaded
parts of the APB block diagram shown in Figure 6. The audio codec is a common audio
electric component and for our experimentation, we tested multiple codec devices that have
differing degrees of complexity and capability. The MAX5556 provided the simplest
interface and costs $1.84 [16]. The NXP UDA1342TS audio codec permits the software
control of the output volume though an independent I2C serial interface and costs $3.16 [17].
The NXP UDA1380 stereo audio coder-decoder integrated circuit provides the capability to
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Improving Pedestrian Safety at Signalized Intersections 12
provide both digital to analog conversion and analog to digital conversion in a single silicon
package for only $1.23 [18].
NXP ARM Processor
VDD
Pedestrian
Push Button
Remote
Pedestrian
Control
Acknowledge
Call LED
EoP
Modem
Power
Converter
MPedestrian
Push Button
Vibrator
System Power &
Communications
Dual Audio Amplifier
Microphone
Amplifier
Audio Speakers
Microphone
Audio
Codec
Aux Digital
IO
Figure 6. Block diagram of Advanced Pedestrian Button with added capability for second speaker
The audio output amplifier currently used in the APB is the LM4755 integrated circuit
originally produced by National Semiconductor but currently marketed by Texas Instruments
[19]. Since the audio codec uses a serial binary interface, the original APB circuit was not
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Improving Pedestrian Safety at Signalized Intersections 13
modified during testing. Instead, two of the auxiliary digital outputs were used to interface
with each of the codec units described above.
Passive Pedestrian Detection
The use of passive detection in conjunction with AAPS was tested. Our research focused of
the interface of the Safewalk and Traficam systems marketed by Traficon USA [3,4]. The
two units were set up in the UI pedestrian research laboratory by affixing the units to the
ceiling support I-beam located approximately 10 feet above the floor. Conductors containing
a twisted pair of #18 stranded wire were used to connect the Safewalk and Traficam
detection outputs to one of the auxiliary digital IO pins of the NXP processor illustrated in
Figure 6. Figure 7 shows the circuit used for this interface. Depending upon which IO pins
are used, the NXP processor can be programmed to detect the contact closure in the passive
detection devices using either processor interrupts or by polling the IO pin and determining
the logic level.
Processor
IO Pin
VDD
Pull Up
Resistor
Passive
Detection
Device
Output
Twisted pair
cable
Figure 7. Passive detection interface circuit
The network packet that is sent from the APS to the APC when a pedestrian pushbutton press
is detected was modified. Additional bits in the packet byte that contained the pedestrian
button call type are programmed to identify the passive detection input status. The modified
detection software now generates an unsolicited User Data Protocol (UDP) message
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Improving Pedestrian Safety at Signalized Intersections 14
whenever a pedestrian button press is detected or the relay contact closes on either passive
detection device.
Preemption and Pedestrian Signals
The APC shown in Figure 2 is capable of sensing 16 load switch outputs to monitor the
WALK and DON’T WALK signal status using MID400 optically isolated AC voltage
detector integrated circuits. Two additional inputs that also use the MID400 IC are allocated
for AC or DC voltage detection, and the logic outputs can be read by the APC processor as
shown in Figure 8. AC or DC voltage input to the MID400 is set by selecting the value of R1
as described in the product datasheet [20]. The ACS3 can be programmed to output a signal
that indicates that a preemption sequence has been initiated.
AC
VDD
R1 R2
C1
MID400
F1
SW
Preemprion Test
Circuit
APC Interface
Circuit
To I2C IO
Buffer
MO
V
Figure 8. Preemption test circuit and APC AC sense circuit
To determine the best visual and audible message to display to pedestrians, surveys were
conducted to collect data from actual users. Undergraduate students completed an initial
survey to determine the symbol that best portrays that an emergency vehicle is approaching
the intersection. From this survey, the eight symbols for each emergency vehicle (police car,
fire engine, ambulance) were reduced to five. The researchers then made an educational visit
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Improving Pedestrian Safety at Signalized Intersections 15
to a local school where we talked about the safety of crossing streets, distracted drivers and
pedestrians, and had the 6th
grade students complete the revised survey on emergency vehicle
symbols. We felt it was important to include children since they can be pedestrians as well
and would need to interpret the symbols just as older pedestrians would. From the results of
the 6th
graders, it was obvious there were some issues with a few of the symbols. We then
revised the survey once again and included more detailed ambulance symbols. This survey
was taken by additional undergraduate students to help narrow the possibilities to three.
In addition, a preliminary survey on audible preemption messages was given to engineering
students. The messages varied from a simple “Clear intersection” to a more complex message
“Emergency vehicle approaching, clear intersection” with a siren included.
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Improving Pedestrian Safety at Signalized Intersections 16
FINDINGS; CONCLUSIONS; RECOMMENDATIONS
The following results were determined by analysis of experimental data, weekly phone
conference meetings involving UI researchers and Campbell Company engineers, and by
verbal feedback given at the PED ACCESS 2012 WORKSHOP, Boise ID, May 5, 2012. The
meeting agenda and notes of the workshop are provided in the appendix.
Audio Beaconing
Audio beacons are intended to supplement crosswalk signs and markings. For the low-vision
public, determining the destination curb is a daunting task and made even more daunting if
the intersection has unusual geometries. The pedestrian route can be difficult if markings are
obscured by snow, worn off the street by traffic, or unobservable by lack of light or loss of
sight. Pedestrian signals can be difficult to read when the signals are placed at a considerable
distance or obscured by background visual noise created by street lighting, business
advertisements, and ornamental lighting.
The use of audio tones and/or messaging is effective for helping pedestrians who have a wide
range of abilities. This group includes children, young adults, adults, and elderly pedestrians
whenever they have difficulty in determining the point of destination. It was reported in the
2011 TRB Pedestrian Workshop in Washington DC that audio beaconing is as effective of a
navigational aid as raised markings on the street surface. One suggestion under consideration
is the use of the audible countdown as the audible beacon. This idea combines both
navigational information and information concerning task completion time in the same
audible message.
The current version of APS has implemented beaconing using a single speaker positioned as
suggested by the MUTCD. Feedback from the PED ACCESS Workshop suggests that a
second speaker is required to direct the audible beacon to be most effective. Laboratory
experiments have shown that the second speaker can be added to the current APB design
using low-cost electronic hardware components and minor modifications to the current ABP
computer code. Additional power consumption is required to power the second speaker.
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Improving Pedestrian Safety at Signalized Intersections 17
Implementation challenges with audio beaconing include managing multiple audible
messages from the same source point in a manner that will not confuse or distract
pedestrians. Selective activation restricting the use of audio beacons to only select
intersections and for APS (extended press) calls will minimize complaints from any
unintended audience.
The placement of the beacon speaker was not investigated during this research. Placing the
beacon speaker at head level will give higher directionality, provided the speaker is mounted
where the crosswalk meets the curb. The potential problems with the low-level placement
center on distortion due to acoustic echoes. The elevated speaker location can be
accomplished by providing an audio jack or fixed wiring. Either method has cost and
reliability implications.
In conclusion, audio beaconing has a high benefit to cost ratio and this capability will be
integrated into the design of the second generation AAPS.
Passive Pedestrian Detection
The Traficon passive pedestrian detection devices have the potential to provide improved
access for low vision and mobility handicapped pedestrians. The system may provide safety
advantages when used for school crossings or near homes for the elderly. We defer to other
research to define the proper deployment of pedestrian detection systems [14, 21, 22, 23].
The use of passive pedestrian detection may address the need for the “extra press” option
needed to mitigate loss of the walk cycle due to excessive orientation time or late-in-cycle
pedestrian calls for low-vision pedestrians.
The equipment provides a contact closure whenever a person is detected in the programmed
detection area, whether that is on the curb or in the crosswalk. The low technology binary
output renders a simple interface, with AAPS and APB units requiring minimal circuit
modification. No equipment failures were observed during laboratory experiments using the
SafeWalk and Traficam devices.
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Improving Pedestrian Safety at Signalized Intersections 18
We conclude from our investigation that integration of a passive detection system is feasible
should the specific situation arise that justifies the expense of the additional equipment.
Preemption and Pedestrian Signals
The capability of the APC to detect a preemption input was tested in the UI Digital
Laboratory by simulating a switched 120V AC signal as shown in Figure 8. Software
modifications in the APC and APB units were necessary to allow the status of the preemption
inputs to be communicated with the pedestrian stations around the intersection. The APBs
can be programmed to respond to these signals. Even though various traffic agencies have
requested this capability, to date, no agency has specified the exact content of the preemption
message or what the response of the AAPS should be. Clearly, there is an expectation by the
traffic industry that something should be done, but the correct thing to do has not been
determined.
The final surveys indicated that three symbols were significantly preferred for the fire engine
and ambulance (Figure 9 and Figure 10, respectively). However, there was only one symbol
was significantly preferred for the police car as is seen in Figure 11. The surveys will once
again be revised to include only three symbols for each vehicle and administered to
pedestrians of all ages. The idea is that these symbols should be recognizable to all
pedestrians. Symbols relating to rail trains will be examined in the future.
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Improving Pedestrian Safety at Signalized Intersections 19
Figure 9. Results for the fire engine preemption symbol (* indicates significantly different at 95%)
Figure 10. Results for the ambulance preemption symbol (* indicates significantly different at 95%)
1 2 3 4 5
1 2 3 4 5
*
* *
*
*
*
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Improving Pedestrian Safety at Signalized Intersections 20
Figure 11. Results for the police car preemption symbol (* indicates significantly different at 95%)
Since a big part of designing the pedestrian signals for all users includes the blind and low
vision users, the use of an audible preemption message must also be examined. Results from
the preliminary survey shown in Table 1 indicate that finding a “correct” message may be
difficult without more guidance from traffic engineers or the blind pedestrian community.
Further studies on audible messages should be conducted to find the best message as well as
include various age groups to examine understanding. Additional experiments would include
location of the speakers (related to beaconing), loudness of the message, and conjunction of a
visual and audible message.
Table 1. Results from the preemption audible message survey
Message Number of
Respondents
Percent of
Respondents
Clear intersection 2 5.7
Emergency vehicle approaching, clear intersection 15 42.9
Emergency vehicle approaching 10 28.6
Emergency vehicle, clear intersection 8 22.9
1 2 3 4 5
*
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Improving Pedestrian Safety at Signalized Intersections 21
The preliminary results and feedback from the blind community as well as those in the
transportation field indicate that some form of a preemption warning is needed. The cost is
low with a high benefit, making it worthwhile to pursue.
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Improving Pedestrian Safety at Signalized Intersections 22
APPENDIX
PED ACCESS WORKSHOP AGENDA
May 4, 2012
8:30 – 9:00 a.m. Coffee and donuts
9:00 – 10:15 a.m. Welcome, introductions and workshop notes (Richard and Phil)
10:15 – 11:00 a.m. AAPS
1. Review of Smart Signals (Richard)
2. Web site for Research Activity (Karen)
3. Recent Research Activity
a. Pedestrian Fault Monitor (Ben)
b. SDLC Interface (Jacob)
11:00 – 11:10 Break
11:10 – 12:00
4. Changes in MUTCD and APS (Phil)
a. Advisor independent APS
12:00 – 12:30: Lunch and visits
12:30 – 1:30
5. AAPS Features and Controls (Cody)
1:30 – 2:00
6. Preemption notification (Denise)
7. Pedestrian community Input
2:00 – 2:15 Break
2:15 – 3:00
8. Pedestrian safety – accessibility for people with barriers and vision limitations
a. Traffic – pedestrian interface and coordination
b. Operations and maintenance (traffic agencies)
c. Users – what helps – what doesn’t
d. Wish list
3:00 – 3:15 Future work (Richard)
3:15 – 3:45 Where to go – action items
a. Identify key issues
b. Cost benefit discussion
c. Prioritize effort
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Improving Pedestrian Safety at Signalized Intersections 23
3:45- 4:00 Wrap up (Richard and Phil)
4:00-5:00 Plant Tour
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[2] “SafeWalk - The First Stereovision Video Sensor”, manufactured by Traficon Video Detection,
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[3] “TrafiCam – The First Integrated Video Sensor”, manufactured by Traficon Video Detection,
http://www.traficon.com/pagenode.jsp?id=6&type=ProductCategory.
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Improving Pedestrian Safety at Signalized Intersections 24
[12] “Dangerous by Design 2011”, Transportation for America, available at http://t4america.org/docs/dbd2011/Dangerous-
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[14] ”Selecting the Most Effective ITS Application for Pedestrian Safety”, Report prepared for the Florida Department of
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[16] MAX556 Low-Cost Stereo Audio DAC Datasheet, datasheet available for download at http://datasheets.maxim-
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[17] UDA1342TS Audio Codec, NXP Semiconductor, datasheet available for download at
http://www.nxp.com/documents/data_sheet/UDA1342TS.pdf.
[18] UDA1380 Stereo Audio Coder-Decoder for MD, CD, and MP3, NXP Semiconductor, datasheet available for download
at http://www.nxp.com/documents/data_sheet/UDA1380.pdf.
[19] LM4755 Stereo 11W Audio Power Amplifier with Mute Data Sheet, Texas Instruments Semiconductor, datasheet
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[20] MID400 AC Line Monitor Logic-Out Device data sheet, Fairchild Semiconductor, datasheet available at
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[21] “Passive Pedestrian Detection”, Accessible Pedestrian Signals – a Guide to best Practices, Chapter 4. Available for
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[23] “Pedestrian Safety - Report to Congress”, US Department of Transportation Federal Highway Administration, August
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